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| author | Simon Riggs <simon@2ndQuadrant.com> | 2012-12-03 11:59:25 +0000 |
|---|---|---|
| committer | Simon Riggs <simon@2ndQuadrant.com> | 2012-12-03 11:59:25 +0000 |
| commit | 1c563a2ae1c800c93fe5f41d0427e36bef874ba7 (patch) | |
| tree | 05bc10d74e08e9c6472ea4905b9ed96247aad68d | |
| parent | a068c391ab0c3f2d3487fd3090a769cc5cb19ba9 (diff) | |
| download | postgresql-1c563a2ae1c800c93fe5f41d0427e36bef874ba7.tar.gz postgresql-1c563a2ae1c800c93fe5f41d0427e36bef874ba7.zip | |
Clarify when to use PageSetLSN/PageGetLSN().
Update README to explain prerequisites for
correct access to LSN fields of a page.
Independent chunk removed from checksums
patch to reduce size of patch.
| -rw-r--r-- | src/backend/access/transam/README | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/backend/access/transam/README b/src/backend/access/transam/README index f8ebf5758f0..548ddbb4dd5 100644 --- a/src/backend/access/transam/README +++ b/src/backend/access/transam/README @@ -564,6 +564,14 @@ something like if (BufferIsValid(buffer0)) UnlockReleaseBuffer(buffer0); +Note that we must only use PageSetLSN/PageGetLSN() when we know the action +is serialised. Only Startup process may modify data blocks during recovery, +so Startup process may execute PageGetLSN() without fear of serialisation +problems. All other processes must only call PageSet/GetLSN when holding +either an exclusive buffer lock or a shared lock plus buffer header lock, +or be writing the data block directly rather than through shared buffers +while holding AccessExclusiveLock on the relation. + Due to all these constraints, complex changes (such as a multilevel index insertion) normally need to be described by a series of atomic-action WAL records. What do you do if the intermediate states are not self-consistent? |